The steering mechanism of a motor vehicle, provided between the steering wheel and the steering box, comprises an intermediate shaft typically formed basically by a male member or steering column and a female member designed to be telescopically received into the male member.
The main function of the intermediate shaft of the steering column of a motor vehicle is to adjust the position of the steering wheel in depth to adapt it to the driver's size, as well as to act as a safety means allowing the collapse in the event of an accident. Another function of said shaft is to take up vibrations which may arise from the wheels and suspension to the steering wheel. The intermediate shaft performs the function of collapse means so that, in the event of an accident, the male member is collapsed into the female member due to the provision energy absorption means.
The use anti-vibration joints between the male member and the female member responsive to heat may result in a variation in the friction force between both, as the intermediate shaft is provided into the interior space for the engine, which result, in extreme situations, in that the joint does not perform its function as it is either shrunk or its size becomes increased when expanding.
The prior art provides several intermediate shaft configurations, all of them with a view to allow a relative movement between the male member and the female member with controlled sliding load in the event of crash. Therefore, said energy absorption means are provided which allow generating a resistance to the relative movement of the male member and the female member.
A typical configuration of the intermediate shaft consists of a male member and a female member both having a polygonal, for example triangular, cross section between which rollers or balls are provided in contact with the female member inner faces and the male member outer faces for enabling the relative slippage therebetween. Thus, there are always two active faces before a stress with the purpose of achieving a steering system proper operation.
The main disadvantage of this type of configuration is that it is expensive due to the provision of rollers or balls along the male and the female members of the intermediate shaft at the same time determined tolerances is difficult to obtain.
Another disadvantage of this type of state of the art solutions is the high moment of inertia in this type of systems using rollers or balls. The moment of inertia is initially very high and after the impact it is quickly reduced. The initial resistance sensed by the driver at the beginning is too high and consequently the impact absorption effect on the driver is not completely effective.